Storage tank for cold liquids, and method for applying a thermal insulation system in such tank

ABSTRACT

A double containment storage tank, suitable for storing cold liquids, is provided with a non-metallic thermal protection system. The storage tank can include a first vapour-tight and gas-tight PU coating applied by spraying on the inner surface of the floor and walls of the tank; a first insulation PU foam layer arranged on the inner side of the first coating; a second liquid-tight PU coating applied in at least the bottom corner sections of the tank by spraying on the inner surface of the first foam layer; a second insulation PU foam layer arranged on the inner side of the second coating; and a third liquid-tight PU coating arranged by spraying on the inner side of the second foam layer.

FIELD OF THE INVENTION

The present invention relates in general to the field of storing coldliquids in a large storage tank. Typical operation conditions of suchstorage tanks are in the range of 0° C. to −200° C. More particularly,the present invention relates to tanks intended for storing substanceswhich are liquid in the temperature range between −5° C. and −196° C.,wherein storage takes place under atmospheric pressure. For storagetanks of this type, a Euro-norm applies, indicated as “atmospheric,refrigerated, liquefied gas storage tanks with operating temperaturesbetween −5° C. and −196° C.”. Such tanks are fixedly positioned at astorage location, either above bottom surface or sunken completely inthe bottom. Horizontal dimensions of such tanks are typically within therange of 10meters to 100 meters, and the height can typically be up to50 meter.

Still more particularly, the present invention relates to tanks intendedfor storing liquid LNG, having a temperature in the range of −102° C. to−165° C.

BACKGROUND OF THE INVENTION

Tanks for storing such cold liquids, indicated hereinafter as “coldstorage tanks”, have to meet a number of design requirements. Theconstructive strength should be large enough to carry the weight of theliquid, and to withstand the forces that occur in the case of anearthquake. The tank should be liquid-tight, vapor-tight, and shouldfulfill an isolating function between the surroundings and the coldliquid in the interior. Finally, provisions must be made to prevent thatthe tank immediately empties completely towards the surroundings in theunlikely event of a leakage of the tank.

Known cold storage tanks are built according to one of the followingconcepts.

A first tank concept, indicated as “tank-in-tank” concept or “fullcontainment tank” concept, comprises an inner vessel arranged in anouter vessel. The outer vessel is typically made from reinforcedconcrete. The inner vessel can be made from concrete or cryogenicresistant steel. The inner surface of the concrete outer vessel isprovided with a metal plating to serve as a vapour barrier and gasbarrier. Furthermore it is provided up to a certain height with acryogenic metal plating on top of an insulating layer to serve as athermal corner protection of the concrete, indicated as secondary liner.In this first tank concept, the functions mentioned above are fulfilledby different components. The inner vessel contains the cold liquid. Inthe unlikely event of a leakage of the inner vessel into the outervessel, the secondary liner prevents the cold liquid from reaching theouter concrete vessel, especially the corner area thereof. The spacebetween the inner vessel and the outer vessel is filled with insulationmaterial. This secondary liner makes the tank to be of a “fullcontainment type”.

A second tank concept, indicated as “membrane tank” concept, has a thinmetal plating or membrane attached to a load-bearing insulation, whichagain is attached to the inner surface of the outer vessel over theentire height of the outer vessel. This tank has no separate innervessel as the membrane fulfils the functions of the inner vessel. Themembrane has a complicated profile in order to allow expansion andcontraction caused by the temperature changes. It is noted that thistank also has incorporated a secondary liner by means of a triplex foilwithin the load-bearing insulation to obtain the status of a “fullcontainment type”.

When building such a tank according to the first tank concept, first theouter vessel is built. During the construction of the walls, a largedome-shaped carbon steel roof is built within its perimeter and, whenthe walls are finished, the roof is hoisted or blown to the top of thewalls and fastened to close the tank. Then, metal plates are arranged atthe inner side of the concrete bottom and walls and are welded toanchoring points in the concrete walls and to each other as well as tothe carbon steel roof in order to provide for a vapour-tight andgas-tight enclosure. A first insulation layer is arranged on the bottomof the outer vessel, and also on part of the wall. The insulation is inthe form of cellular glass, which material only reaches the desiredpressure resistance with special bitumen products. Also PVC foam can beused. A ringbeam is now installed onto this insulation layer to supportthe inner vessel. Inside the ringbeam, additional insulation layers areapplied to obtain the desired insulation value. The inner vessel is nowbuilt on top of the bottom insulation and ringbeam. The first insulationlayer in the annular space and onto part of the wall is now covered by acryogenic resistant metal plating of Invar or 9% Nickel steel to act asa liquid-tight secondary liner. These steel plates must be made tomeasure on location and must be welded to each other and the inner tankin a liquid-tight manner.

On top of the inner vessel, a suspended ceiling is hung from thedome-shaped roof and completely covered with a substantially thick layerof fibre-glass insulation.

Then, insulation material is arranged in the space between the wall ofthe inner vessel and the wall of the outer vessel. This insulationcomprises a resilient glass fibre blanket against the wall of the innertank, and the rest of the annular space is filled by pouring perlitegrains.

Thus, building such a tank according to the state of the art is verylabour-intensive. Herein it is the disadvantage that applying severaldifferent kinds of insulation material and sealing material at theseveral locations must be done at strongly different moments in time,while furthermore those activities lie on the Critical path, i.e.subsequent activities must wait until previous activities have beencompleted.

During use, especially the inner vessel will experience volumevariations as result of thermal contraction and changing liquid loadlevels. This has as a consequence that the dimensions of the annularspace between the inner vessel and the outer vessel vary, causing theconventionally used perlite grains to tend to settle themselves, i.e.the height of the perlite bulk decreases. In order to maintain thedesired insulation value, therefore, perlite must regularly be filled.The resilient glass fibre blankets are to reduce the settling of theperlite grains, but still do not prevent the necessity of a regularlyfilling of perlite.

When building such a tank according to the second tank concept, i.e. a“membrane” tank, first the outer vessel is built. During theconstruction of the walls, a large dome shaped carbon steel roof isbuilt within its perimeter and, when the walls are finished, the roof ishoisted or blown to the top of the walls and fastened to close the tank.Then, prefabricated insulation panels comprising of PVC or polyurethaneload-bearing insulation between two plywood outer surfaces are fastenedto the outer concrete vessel using load-bearing mastics to accommodatefor the curvature of the tank. Thin steel membrane plates are thenanchored to the plywood inner surface and welded together. In order toobtain a full containment status, the prefabricated insulation panels ofthe bottom and lower wall part incorporate a secondary liner within thepanels of a triplex foil.

Also the membrane tank uses a suspended ceiling hung from thedome-shaped roof and completely covered with a substantially thick layerof fibre-glass insulation.

Thus, building such a tank according to the state of the art requiresvery accurate manufacturing processes using special ply-woods,adhesives, expensive insulation materials. The anchoring of the ply-woodpanels to the concrete outer vessel, the jointing of the secondary linerof triplex foil on the job-site and the complexity of welding thecomplicated profiles of the steel membrane makes the entire constructionof such a tank very labour-intensive and requires the use of veryskilled labour.

A general disadvantage of these two types of tanks is to be seen in theneed of handling and welding metal plates for manufacturing the linerand attaching the liner to the wall of the outer vessel, and weldingmetal plates of the inner tank or the membrane tank. WO-02/29310, thecontents of which is incorporated herein by reference, has proposed amethod for building a storage tank which avoids the need of metalplates. In the storage tank of this publication, which can be indicatedas a third type of tank, PVC-foam plates provided with a coatingprovided with gravel are attached to the inner side of the concrete wallof the tank. Over the PVC-foam, a monolithic coating layer is applied.On the bottom of the tank, a first coating layer is applied; thenPVC-foam blocks are arranged, and finally a monolithic coating layer isapplied. The coating layers are sprayed.

The third type of tank, and its building method, as proposed byWO-02/29310 already has major advantages over the first and second typesof tank. Nevertheless, further improvements are possible.

An important aim of the present invention is to provide a still furtherimproved tank concept.

More particularly, the present invention aims to provide a design andbuilding method for a storage tank for cold liquids, wherein asubstantial saving on building time and building cost can be achieved,while maintaining or perhaps even improving the insulation propertiesand the sealing properties.

SUMMARY OF THE INVENTION

According to an important aspect of the present invention, the wall andfloor of a cold storage tank are provided, at the inside, with amultilayer sprayed insulation comprising at least a layer ofpoly-urethane foam sandwiched between two sprayed layers ofpoly-urethane coating.

The layer of poly-urethane foam may entirely or partly be made fromblocks, but preferably the layer of poly-urethane foam is also sprayed,in which case the entire insulation structure is applied by spraying,which achieves an enormous saving of building time and labour.

Further, all layers of the insulation structure are made fromsubstantially the same material, so the insulation structure as a wholebehaves as a monolithic layer.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, features and advantages of the presentinvention will be further explained by the following description withreference to the drawings, in which same reference numerals indicatesame or similar parts, and in which:

FIGS. 1-6 are cross sections schematically illustrating subsequent stepsin a method for building a cold storage tank in accordance with thepresent invention;

FIG. 7 schematically illustrates an anchor point.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 schematically illustrates a first step in a building process forbuilding a cold storage tank 1. In this first step, a concrete floor 11and concrete walls 12 are built, in a conventional manner. The walls 12and floor 11 meet in corner areas 13.

As a next step, illustrated in FIG. 2, a first coating 21 is applied atthe inner surfaces of the floor 11 and the walls 12, preferably, asshown, over the entire height of the walls 12. The first coating 21 is apoly-urethane material (PU), applied by spraying, to a suitablethickness of about 3 mm. The first coating 21 will function as a vapourbarrier and gas barrier, and is adapted to be vapour-tight andgas-tight. It is also liquid-tight.

As a next step, illustrated in FIG. 3, a first PU foam layer 22 isapplied on the inner surface of the coating 21. The first PU foam layer22 may be applied over the full height of the walls 12 but, preferably,as shown, the first PU foam layer 22 is applied on the floor part of thecoating 21 and up to a certain height on the wall part of the coating21.

Although parts of the first PU foam layer 22 may be applied asindividual blocks, the first PU foam layer 22 is preferably applied byspraying, to a suitable thickness in the order of about 150 mm or more.In view of this thickness, the first PU foam layer 22 may actually beapplied as a succession of multiple layers. The first PU foam layer 22will function as an insulation.

As a next step, illustrated in FIG. 4, a second PU coating 23 is appliedon the inner surface of the first PU foam layer 22. The second PUcoating 23 is applied by spraying to a suitable thickness of about 3 mm.The second PU coating 23 will function as a liquid barrier, and isadapted to be liquid-tight. Although the second PU coating 23 may beapplied over the entire height of the walls 12, this is not alwaysnecessary. In case the first PU foam layer 22 extends over only part ofthe height of the wall 12, as illustrated, the second PU coating 23should extend higher than the first PU foam layer 22 and should mergewith the first PU coating 21. Thus, the first PU foam layer 22 iscompletely encapsulated by PU coating 21, 23, in order to assure thatthe first PU foam layer 22 remains dry.

As a next step, illustrated in FIG. 5, a second PU foam layer 24 isapplied on the inner surface of the first PU foam layer 22 and thesecond PU coating 23, preferably, as shown, over the entire height ofthe walls 12. Although parts of the second PU foam layer 24 may beapplied as individual blocks, the second PU foam layer 24 is preferablyapplied by spraying. The second PU foam layer 24 will function as aninsulation, together with the first PU foam layer 22. The combinedthickness of the first PU foam layer 22 and the second PU foam layer 24is suitably in the order of 300 mm or more. Thus, in locations where thefirst PU foam layer 22 is present, the thickness of the second PU foamlayer 24 is reduced, whereas in locations above the first PU foam layer22, the thickness of the second PU foam layer 24 preferably is in theorder of 300 mm or more. In view of this thickness, the second PU foamlayer 24 may actually be applied as a succession of multiple layers.

As a next step, illustrated in FIG. 6, a third PU coating 26 is appliedon the inner surface of the second PU foam layer 24, preferably,as-shown, over the entire height of the second PU foam layer 24. Thethird PU coating 26 is applied by spraying to a suitable thickness; athickness of about 4-5 mm is adequate, although a thickness of about 3mm is usually sufficient. The third PU coating 26 will function as amembrane, and is adapted to be liquid-tight.

Placing a roof on top of the tank can be done by conventional buildingmethods, so this needs not be explained in further detail. It is noted,however, that the roof, once built, can be sprayed with foam and/orcoating PU as well.

It is possible to place an inner vessel inside the tank 1 thus built, ifdesired, in which case the cold liquid would be contained in the innervessel only. However, the tank-in-tank concept has disadvantages, asmentioned above, while further the tank-in-tank concept does not fullyutilize the storage capacity of the tank. An important advantage of thetank 1 is that the tank 1 itself is suitable to act as cold liquidcontainer, without a separate inner vessel being necessary. Then, inoperation, the cold liquid (not shown for sake of simplicity) would bein contact with the third PU coating 26. The first PU foam layer 22 andthe second PU foam layer 24 together act as thermal insulation betweenthe cold liquid contents and the concrete floor 11 and walls 12, thefirst PU coating 21 and the third PU coating 26 (the thickness of whichis exaggerated in the figures) also contributing insulative capacity.The third PU coating 26 acts as membrane, protecting the foam 24 againstentry by the cold liquid. The first PU coating 21 acts as barrier,protecting the foam 22, 24 against entry by moist or vapour whichpenetrates from the surroundings through the concrete floor 11 and walls12.

Under normal circumstances, the second PU coating 23 does not need tocome into action. Only in case of a leakage of the third PU coating 26(and leakage of a possible inner vessel), cold liquid will enter thefoam 24, and will ultimately reach the second PU coating 23. If thesecond PU coating 23 would be absent, the cold liquid would be separatedfrom the concrete floor 11 and walls 12 by the first PU coating 21 only.In principle, this separation is sufficient in that no cold liquid willleak through to the concrete; in any case, the first PU coating 21 isliquid-tight. However, the thermal insulative capacity of the first PUcoating 21 alone is insufficient for protecting the concrete so that, insuch circumstances, the concrete would cool down to a very lowtemperature; as a consequence, the risks of concrete cracks increase.These risks are largest in the corner areas 13 of the tank 1, i.e. wherethe walls 12 and floor 11 meet. The second PU coating 23, physicallyseparate from the third PU coating 26, now acts as an additionalprotection for these corners, keeping the cold liquid away from thesecorners, maintaining at least the first PU foam layer 22 operational asprotective insulation between the concrete and the cold liquid.

It is noted that it is best to protect the entire floor 11 and at leasta part of the walls 12 (depending on the height of cold liquid to beexpected in a worst-case scenario) against the very low temperatures, soit is preferred that the second PU coating 23 extends over the entirefloor 11, as illustrated. However, since the potential problems causedby cold liquid are largest in the corner areas 13, it may, depending ondesign, be sufficient if the second PU coating 23 (and the first PU foamlayer 22) is arranged in the corner area only: in that case, the secondPU coating 23 would extend beyond the first PU foam layer 22 and mergewith the floor part of the first PU coating 21, as indicated by a dottedline 23′ in FIG. 4, to keep the first PU foam layer 22 encapsulated.

So, the second PU coating 23 acts as a backup for the third PU coating26, having the same mechanical properties as the third PU coating 26.The second PU coating 23 should be separate from the third PU coating 26in order to prevent possible failures in the third PU coating 26 fromdamaging the second PU coating 23. The second PU coating 23 maintainssufficient insulation (i.e. first PU foam layer 22 remaining dry insteadof being drenched with cold liquid) between cold liquid and concrete. Itis possible to protect the entire height of the walls 12 in this way, byhaving the first PU foam layer 22 and the second PU coating 23 extendover the full height of the walls 12.

For actually maintaining sufficient insulation, it is preferred that thefirst PU foam layer 22 is as thick as possible. In a suitableembodiment, the thickness of the first PU foam layer 22 is chosen in therange 150-250 mm, while the thickness of the second PU foam layer 24 ischosen in the range 150-50 mm, the combined thickness beingapproximately 300 mm.

The main advantages of the present invention are associated with thebuilding process. Once the concrete floor has been laid and the concretewalls have been erected, the entire thermal protection system can beapplied by spraying, using in principle the same material (PU) for alllayers. Since only one appplication technique is used, the work can bedone by only one construction company (sub-contractor), which is muchmore efficient than having to coordinate different teams of worksmenperforming different works on necessarily pre-defined times.

Especially, it is an advantage that the thermal protection system doesnot need to contain any metal parts any more.

It is also an advantage that all thermal protection layers are made fromthe same material or material family (poly urethane), so that all layershave identical or at least comparable thermo-mechanical properties suchas expansion/ contraction coefficient.

A material which can very advantageously be used as gas-tight andliquid-tight coating in the present invention is a two-component polyurethane composition which is commercially available from the companyTAGOS S. r. L. in Busto Arsizio, Italy, under the brand name IWR ESATECHR 1000. In the market, this material is also known under the name IWRCRYOCOAT HR, and is commercially available under this name from thecompany INSU-W-RAPID B.V. in Tilburg, the Netherlands. The coatingmaterial is sprayed by means of a mix/spray head, and the componentsimmediately undergo a chemical reaction which is finished afterapproximately 2 minutes, after which a further layer can be applied. Ineach spraying cycle, the thickness of the layer to be applied can be setas desired. A suitable value for the thickness of the layers to beapplied is in the range of 2-4 mm, but it is possible to apply thinneror thicker layers. It is noted that, in the figures, the thicknesses ofthe different layers are not shown to scale.

It is possible to build the thermal protection system over the entiretank as a whole, i.e. to apply one layer over the entire inner surfaceof the tank, to apply a second layer over the entire inner surface ofthe tank, etc. In a preferred embodiment of the present invention, it ispossible to apply the entire thermal protection system in one section ofthe tank wall, and then apply the entire thermal protection system in anadjacent section, etc. Suitably, such section may extend over the entireheight of the wall and have a width in the order of a few meters. Thus,it is possible to confine the work to one part of the tank while otherwork may be done in another part of the tank, without the workers beingin each others way.

As regards the insulating foam, to be used for the foam layers 22 and24, it is noted that poly-urethane foams are suitable if such foam has asufficiently high coefficient of thermal stress resistance, indicated asCTSR-value. The CTSR is defined according to the following formula:${CTSR} = \frac{\sigma \cdot ( {1 - \gamma} )}{E \cdot \alpha \cdot ( {T_{2} - T_{1}} )}$where:

-   -   σ indicates the tensile strength of the foam at −165° C. (kPa;        minimum value of all three directions);    -   E indicates the tensile modulus of the foam at −165° C. (kPa;        minimum value of all three directions);    -   α indicates the average linear constriction coefficient of the        foam from −165° C. up to +21° C. (maximum value of all        directions);    -   γ=0.4, estimated value for Poisson's ratio at −165° C. (other        values may be used if substantiated by experimental data)    -   T₂−T₁ ₌185° C., estimated value for temperature difference        between cold surface and surroundings        Thus, apart from mechanical design criteria, the density and        chemical formulation of the foam should preferably be selected        in such a way that the CTSR-value is sufficiently high,        preferably in the order of approximately 3 or higher.

It is noted that foam compositions meeting this requirement arecommercially available, so it is not necessary here to give more detailson the composition.

Normally, the fixation of the thermal protection system to the floor andthe walls of the tank is sufficiently strong to withstand forces thatoccur due to temperature variations. However, this fixation is based onadhesion between PU coating 21 and concrete, and it may be preferred toprovide the walls 12 of the tank, and perhaps also the floor 11, withanchor points which offer a mechanical fixation of the PU to theconcrete. Such anchor point should combine mechanical strength withlittle or no thermal conduction.

FIG. 7 is a cross section illustrating an embodiment of a suitableanchor point 100 in accordance with the present invention. The anchorpoint 100 comprises a bush 110, fixed in the concrete of the wall 12,either by being embedded in the concrete when the concrete was beingpoured into a formwork or by being screwed into the concrete after theconcrete has hardened. A suitable material for the bush 110 is glassfiber reinforced polyester, epoxy or phenolic resin which are materialsknown per se.

The bush 110 is provided with a threaded bore, into which a screw rod120 is screwed, so that the screw rod 120 extends substantiallyperpendicularly with respect to the inner surface of the wall 12. Thescrew rod 120 may be made from the same material as the bush 110.

After the first PU coating 21 and the first PU foam layer 22 have beenapplied to the wall 12, a first retaining plate 131 is screwed onto thescrew rod 120, which first retaining plate 131 may be made from the samematerial as the screw rod 120. The first retaining plate 131 is screwedtight against the first PU foam layer 22, thus providing a mechanicalfixation of the combination of the first PU coating 21 and the first PUfoam layer 22. Then, the second PU coating 23 is applied on the first PUfoam layer 22, over the first retaining plate 131.

Then, after the second PU foam layer 24 has been applied, a secondretaining plate 132 is screwed onto the screw rod 120, which secondretaining plate 132 may be made from the same material as the firstretaining plate 131. The second retaining plate 132 is screwed tightagainst the second PU foam layer 24, thus providing a mechanicalfixation of the second PU foam layer 24, while also adding to thefixation of the underlying layers. Then, the third PU coating 26 isapplied on the second PU foam layer 24, over the second retaining plate132.

If desired, if it is considered that the second retaining plate 132suffices, the first retaining plate 131 may be omitted.

If desired, the retaining plate(s) may be screwed so tight that theunderlying foam layers 22 and 24 are compressed.

It should be clear to a person skilled in the art that the presentinvention is not limited to the exemplary embodiments discussed above,but that several variations and modifications are possible within theprotective scope of the invention as defined in the appending claims.

For instance, the vessel of the tank 1, i.e. floor 11 and walls 12, arenot necessarily made from concrete; in an alternative embodiment, theymay be made from a suitable metal. Since metal is vapour-tight andgas-tight, the first PU coating 21 may be omitted in such embodiment,but the first PU coating 21 may also be maintained.

1. Storage tank suitable for storing cold liquids, comprising a floorand walls meeting each other in a corner area, the storage tank furthercomprising a non-metallic thermal protection system on the inner surfaceof its floor and walls, this protection system comprising, at least inthe corner areas, an array of layers arranged on top of each other,namely, seen from the walls towards the inside of the tank: a first foamlayer having good thermal insulation properties; a liquid-tight coatingapplied on the inner surface of the first foam layer; a second foamlayer having good thermal insulation properties, arranged on the innerside of the coating; a liquid-tight coating arranged on the inner sideof the second foam layer; the first foam layer being fully embeddedbetween liquid-tight layers.
 2. Storage tank according to claim 1,wherein the floor and walls are made from a vapour-tight and gas-tightmaterial, for instance metal.
 3. Storage tank according to claim 1,wherein the floor and walls are made from concrete, preferablyreinforced concrete, and wherein said array of layers further comprisesa vapour-tight and gas-tight coating between floor and walls on the onehand and the first foam layer on the other hand.
 4. Storage tankaccording to claim 1, wherein said coating layers are applied byspraying.
 5. Storage tank according to claim 1, provided with anon-metallic thermal protection system on the inner surface of its floorand walls, wherein the thermal protection system comprises: [a] a firstcoating applied by spraying on the inner surface of the floor and wallsof the tank, the first coating being adapted to be vapour-tight andgas-tight; [b] a first foam layer arranged on the inner side of thefirst coating, the first foam layer being adapted to have good thermalinsulation properties; [c] a second coating applied by spraying on theinner surface of the first foam layer, the second coating being adaptedto be liquid-tight so as to be able to act as a liquid-barrier; [d] asecond foam layer arranged on the inner side of the first foam layer andon the inner side of the second coating, the second foam layer beingadapted to have good thermal insulation properties; [e] a third coatingarranged by spraying on the inner side of the second foam layer, thethird coating being adapted to be liquid-tight so as to be able to actas a membrane.
 6. Storage tank according to claim 1, provided with anon-metallic thermal protection system on the inner surface of its floorand walls wherein the floor and walls are made from a vapour-tight andgas-tight material, for instance metal, wherein the thermal protectionsystem comprises: [b] a first foam layer arranged on the inner surfaceof the floor and walls of the tank, the first foam layer being adaptedto have good thermal insulation properties; [c] a second coating appliedby spraying on the inner surface of the first foam layer, the secondcoating being adapted to be liquid-tight so as to be able to act as aliquid-barrier; [d] a second foam layer arranged on the inner side ofthe first foam layer and on the inner side of the second coating, thesecond foam layer being adapted to have good thermal insulationproperties; [e] a third coating arranged by spraying on the inner sideof the second foam layer, the third coating being adapted to beliquid-tight so as to be able to act as a membrane.
 7. Storage tankaccording to claim 6, further comprising: [a] a first coating applied byspraying on the inner surface of the floor and walls of the tank,between floor and walls on the one hand and the first foam layer on theother hand, the first coating being adapted to be vapour-tight andgas-tight.
 8. Storage tank according to claim 1, wherein the firstcoating, the first foam layer, the second coating, the second foamlayer, and the third coating are made from the same material or materialfamily.
 9. Storage tank according to claim 8, wherein the first coating,the second coating, and the third coating have mutually the samecomposition.
 10. Storage tank according to claim 1, wherein the firstcoating, the first foam layer, the second coating, the second foamlayer, and the third coating are made from poly urethane.
 11. Storagetank according to claim 1, wherein, at least in a part of the thermalprotection system, the first foam layer is applied in the form of foamblocks.
 12. Storage tank according to claim 1, wherein, at least in apart of the thermal protection system, the second PU foam layer isapplied in the form of foam blocks.
 13. Storage tank according to claim1, wherein, at least in a part of the thermal protection system, bothfoam layers are applied by spraying.
 14. Storage tank according to claim1, wherein the first coating has a thickness in the range of 1-10 mm,preferably in the order of about 3 mm.
 15. Storage tank according toclaim 1, wherein the first coating extends over the entire surface ofthe floor and over the entire height of the walls.
 16. Storage tankaccording to claim 1, wherein, in the corner area, the first and secondfoam layers have an overall thickness in the range of 100-500 mm,preferably in the order of about 300 mm.
 17. Storage tank according toclaim 1, wherein, in the corner area, the thickness of the first foamlayer is substantially equal to the thickness of the second foam layer.18. Storage tank according to claim 1, wherein, in the corner area, thethickness of the first foam layer is larger than the thickness of thesecond foam layer.
 19. Storage tank according to claim 1, wherein thefirst and second foam layers extend over the entire surface of thefloor.
 20. Storage tank according to claim 19, wherein the secondcoating extends over the entire surface of the floor.
 21. Storage tankaccording to claim 1, wherein the first and second foam layers extendover the entire height of the walls.
 22. Storage tank according to claim21, wherein the second coating extends over the entire height of thewalls.
 23. Storage tank according to claim 1, wherein the first foamlayer extends over only part of the height of the walls and/or over onlypart of the surface of the floor.
 24. Storage tank according to claim23, wherein the second coating extends beyond the first foam layer. 25.Storage tank according to claim 24, wherein said array of layers furthercomprises a vapour-tight and gas-tight first coating between floor andwalls on the one hand and the first foam layer on the other hand, andwherein the second coating merges with the first coating.
 26. Storagetank according to claim 1, wherein the second coating has a thickness inthe range of 1-10 mm, preferably in the order of about 3 mm.
 27. Storagetank according to claim 1, wherein the third coating has a thickness inthe range of 3-10 mm, preferably in the order of about 4-5 mm. 28.Storage tank according to claim 1, wherein the third coating extendsover the entire surface of the floor and over the entire height of thewalls.
 29. Storage tank according to claim 1, further provided withinsulating anchor points for providing a mechanical fixation of thethermal protection system to the floor and walls of the tank. 30.Storage tank according to claim 29, wherein each anchor point comprises:a bush fixed in a wall or a floor, the bush being provided with athreaded bore; a screw rod screwed into the bush; and at least oneretaining plate screwed tight on the screw rod, pressing at least someof the layers of the thermal protection system against the correspondingwall or floor.
 31. Storage tank according to claim 30, wherein an anchorpoint comprises at least two retaining plates screwed tight on the samescrew rod, a first retaining plate being embedded within the thermalprotection system, preferably between a foam layer and a coating layer.32. Storage tank according to claim 30, wherein the bush is made fromglass fiber reinforced polyester; wherein the screw rod is made from aphenolic resin reinforced with glass fibers; and wherein the at leastone retaining plate is made from a phenolic resin reinforced with glassfibers.
 33. Storage tank according to claim 1, wherein each foam layerhas a sufficiently high CTSR value, preferably in the order of about 3or higher.
 34. Method for applying a thermal protection system in a coldliquid storage tank having a floor and walls, the thermal protectionsystem comprising: a liquid barrier membrane for holding the liquid; athermal insulation layer arranged between the membrane and the floor andwalls of the tank; a secondary liquid barrier embedded within thethermal insulation layer; preferably, a vapour-tight and gas-tight linerattached to the inner surface of the floor and walls of the tank;wherein at least at one location of the tank, all layers of the thermalprotection system are applied by a spraying process, preferably byspraying a substance on the basis of poly urethane.